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Bayerische Forschungsstiftung - FOROXIE2

Abstract

Solid oxide fuel cells (SOFC) are of high interest for clean and reliable energy conversion technologies. Ongoing research targets higher conversion efficiencies, lower operating temperatures as well as an increased cell lifetime. State of the art SOFCs based on ScSZ or YSZ (scandia or yttria stabilized zirconia) electrolytes and LSCF (lanthanum strontium cobalt ferrite) cathodes feature lower resistive losses compared to LSM (lanthanum strontium manganite) cathodes, especially at intermediate temperatures below 700 °C. However, LSCF tends to react with YSZ or ScSZ during operation and fabrication. Therefore, a diffusion barrier layer is required to prevent the formation of insulating SrZrO3. For LSCF:YSZ based cells, oxide ion conducting gadolinium doped ceria (GDC)can be used to separate cathode and electrolyte while retaining a low cell resistance. In this work, the formation of thin GDC films by aerosol deposition (AD) and their suitability as diffusion barrier layers are investigated. Commercially available as-received GDC nanoparticles cannot be processed to films by AD. Grain and particle growth as well as a mechanical activation are induced by thermal and mechanical powder pretreatment, observed by SEM and XRD. Crystallite size of untreated powders remains constant during AD indicating that the particle fracturing that is necessary for film formation may not occur. In contrast, a significant decrease in crystallite size between pretreated powders and resulting films is observed. These films with up to 2 μm thickness are well adhering to the ScSZ substrate. ScSZ substrates with GDC AD films on both sides and subsequently added symmetrical screen-printed LSCF electrodes are characterized by impedance spectroscopy and compared to conventional screen-printed GDC barrier layers.